A Rigid Composite Structure with a Superhard Interior Surface

ABSTRACT

A rigid composite structure has a first bore formed in a metallic material and a second bore formed by a super hard interior segment or segments disposed within the first bore. Each segment may be lined adjacent to one another and held under compression within the first bore. The segments may be made of super hard materials such as natural diamond, synthetic diamond, polycrystalline diamond, single crystalline diamond, cubic boron nitrate or other superhard composite materials which exhibit low thermal expansion rates and are generally chemically inert. The resultant rigid composite structure may possess higher tolerances to high pressures and high temperatures within the second bore.

BACKGROUND OF THE INVENTION

This invention relates to composite structures that retain theirstructural integrity despite exposure to the wear erosive and/orcorrosive effects of sudden high pressures, high-pressure frictionforces and high temperatures typically associated with their use,particularly within the interior of the structure. The present inventionmay be especially adapted for use in gun barrels, piston cylinders,pipes or other composite structures where the retention of structuralintegrity despite exposure to such brisant forces is an integralcomponent of their ordinary application.

Gun barrels for example, are structures that have typically beenconstructed of metallic materials that are incorporated to accommodate aprojectile or bullet that may then be propelled out of the barrel as aresult of an exploding cartridge in the breech end of the structure.During this firing process, brisant forces, including high pressure andelevated temperatures, resulting from the hot gases released from thecartridge and friction and distortion energy created between the bulletand internal circumference of the barrel, are suddenly exerted on thebarrel as the bullet travels along and out of the barrel. Gun barrelsthat are consistently exposed to these brisant forces, such as machinegun barrels that expend hundreds of rounds per minute, are more prone tolosing their original structural integrity as the metallic materialbegins to expand and warp as a result of elevated temperatures exertedon the barrel or the barrel becomes clogged with an accumulation of leadand/or copper that breaks away from projectiles as they exit the barrel.This is of particular concern in gun barrels where the diameter of thebarrel expands such that the internal circumference of the barrel nolonger holds enough compression to effectively launch a projectile, orthe projectile falls short of the desired distance, rendering the gunineffective. Alternatively, gun barrels have also been known to explodeand cause physical injury or death to their operators as a result ofdeformed, warped or clogged barrels. These concerns have becomeincreasingly significant as advancements have been made in ballisticswhich have produced higher powered propellants, higher muzzle velocity,higher rates of fire and so forth, making the probability of thesephenomena more likely.

In response to these phenomena, many attempts have been made to producebarrels made of tough, high strength materials that can accommodate suchadvancements and are capable of withstanding the detrimental effects ofsudden high pressures and temperatures normally associated in ordinanceuse. Despite concerted efforts, many of these developments have yet toprove effective in their application because materials that yield highstrength characteristics may conversely have very low toughnessproperties making the barrel brittle and more susceptible to breaking orexploding, while materials that exhibit high toughness properties mayconversely exhibit low hardness making them more susceptible to erosion.

BRIEF SUMMARY OF THE INVENTION

The present invention is a rigid composite structure that is resistantto wear and able to retain its structural integrity when exposed to hightemperatures and high pressures. This is achieved through theincorporation of high strength, high toughness crystalline materials andtheir subsequent structural arrangement. The structural arrangement andselected materials used serve to enhance the structures low co-efficientof thermal expansion, low friction refractory, high hardness, andchemical inert properties which in turn provide better retention ofstructural integrity and resistance to wear.

The invention comprises a first bore formed in a metallic material. Themetallic material may comprise of one or more of the followingmaterials, including; aluminum, titanium, a refractory metal, steel,stainless steel, Invar 36, Invar 42, Invar 365, a composite, a ceramic,carbon fiber or combinations thereof. In some embodiments, the metallicmaterial may exhibit a low co-efficient of thermal expansion. The firstbore forms a longitudinal axis and encases segments which form a secondbore. The first bore assists to support the segments structurally andmay also be shrink wrapped around the segments to hold it undercompression.

The super hard geometric segment or segments may be arranged co-axiallyadjacent one another within the longitudinal axis of the first bore. Thesegment or segments may comprise natural diamond, synthetic diamond,polycrystalline diamond, single crystalline diamond, cubic boron nitrideor composite materials. These materials may have low thermal expansioncharacteristics and are typically chemically inert which furtherenhances the structures ability to retain its structural integrity. Thesegment or segments may remain in place within the longitudinal axis ofthe first bore being interposed between both a shoulder and biased endof the first bore or by brazing each segment together. The brazedmaterial may comprise of gold, silver, a refractory metal, carbide,tungsten carbide, niobium, titanium, platinum, molybdenum, NickelPaladiium, cadmium, cobalt, chromium, copper, silicon, Zinc, lead,Manganese, tungsten, platinum or combinations thereof. Alternatively,the segments may be held in place by shrink wrapping the first borearound the segments such that the segments are held under radialcompression within the first bore and axial compression along the axisof the first bore.

An intermediate material may serve as a transition layer between thefirst bore and the segments. The intermediate material may comprise ofInvar 36, Invar 42, Invar 365, a composite, a ceramic, a refractorymetal, carbon fiber or combinations thereof. The transition layer mayalso serve as a thermal insulator when wrapped in between the first boreand the segments to reduce thermal expansion of the first bore andassist in maintaining the structural integrity of the compositestructure. In order to promote metallurgical bonding between the firstbore and the segments, as well as the intermediate material, a bindermay be used. The binder may comprise cobalt, nickel, iron, tungsten,tantalum, molybdenum, silicon, niobium, titanium, zirconium, arefractory group metal or combinations thereof.

This new composite structure is capable of withstanding hot, highlycorrosive environments while at the same time also being capable ofwithstanding substantial pressure and structural stresses as a result ofcontinued use and friction, especially within the second bore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective sectional diagram of an embodiment of a rigidcomposite structure in accordance with the present invention broken awayto indicate an indeterminate length.

FIG. 2 is a perspective sectional diagram of another embodimentdepicting a configuration of the super hard segments.

FIG. 3 is a perspective sectional diagram of another embodimentdepicting a configuration of the super hard segments.

FIG. 4 is a perspective sectional diagram of another embodimentdepicting a configuration of the super hard segments.

FIG. 5 is a perspective sectional diagram of another embodimentdepicting a configuration of the super hard segments.

FIG. 6 is a perspective sectional diagram of another embodimentdepicting a configuration for brazing segment interfaces.

FIG. 7 is a perspective sectional diagram of another embodimentdepicting another configuration for brazing segment interfaces.

FIG. 8 is a perspective sectional diagram of another embodimentdepicting another configuration for brazing segment interfaces.

FIG. 9 is a perspective sectional diagram of another embodimentdepicting interlocking configured segments.

FIG. 10 is a perspective sectional diagram of another embodiment as arigid composite structure.

FIG. 11 is an exploded diagram of another embodiment as a rigidcomposite structure.

FIG. 12 is a perspective sectional diagram of another embodimentdepicting a single super hard segment.

FIG. 13 is a perspective sectional diagram of another embodimentdepicting a throat and free bore formed in a super hard compositematerial.

FIG. 14 is an enlarged view of another embodiment depicting a throat andfree bore formed in a super hard composite material.

FIG. 15 is a perspective sectional diagram of another embodimentdepicting a throat and free bore formed in a super hard compositematerial.

FIG. 16 is a perspective sectional diagram of another embodimentdepicting an intermediate layer.

FIG. 17 is a perspective sectional diagram of another embodimentdepicting a threaded receiver.

FIG. 18 is a perspective sectional diagram of another embodimentdepicting a portion of composite material with a threaded receiver.

FIG. 19 is a perspective diagram of another embodiment depicting amethod of subjecting a composite segment to the electrode of an electricdischarged machine (EDM).

FIG. 20 is a perspective diagram of another embodiment depicting amethod of cutting a composite segment using an EDM wire.

FIG. 21 is a perspective diagram of another embodiment depicting amethod of cutting a solid composite segment using an EDM wire.

FIG. 22 is a perspective sectional diagram of another embodimentdepicting a method of forming a pattern in the second bore using an EDM.

FIG. 23 is a perspective sectional diagram of another embodimentdepicting another method of formed in a pattern in the second bore usingan EDM.

FIG. 24 is a perspective diagram of another embodiment depicting a landand groove rifling pattern.

FIG. 25 is a perspective diagram of another embodiment depicting apolygonal rifling pattern.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following, more detailed description ofembodiments of the apparatus of the present invention, as represented inthe Figures is not intended to limit the scope of the invention, asclaimed, but is merely representative of various selected embodiments ofthe invention.

The illustrated embodiments of the invention will best be understood byreference to the drawings, wherein like parts are designated by likenumerals throughout. Those of ordinary skill in the art will, of course,appreciate that various modifications to the apparatus described hereinmay easily be made without departing from the essential characteristicsof the invention, as described in connection with the Figures. Thus, thefollowing description of the Figures is intended only by way of example,and simply illustrates certain selected embodiments consistent with theinvention as claimed herein.

FIG. 1 is a diagram of an embodiment of a rigid composite structure 100in accordance with the present invention. The rigid composite structure100 may comprise a first bore 101 formed in a metallic material andforming a longitudinal axis 106 that is substantially coaxial with asecond bore 102. The second bore may be formed by at least one superhard geometric segment 103 disposed within the first bore. A pluralityof annular super hard composite segments may be interposed adjacent oneanother co-axially along the longitudinal axis 106 of the first bore101. The interior surface of the segments may be polish to provide a lowfriction surface as well.

A significant feature of this invention is the second bore 102 which maybe formed in super hard geometric segments 103 which have a super hardinterior surface 104. The surface may comprise a suitable compositematerial including but not limited to natural diamond, syntheticdiamond, polycrystalline diamond, single crystalline diamond, or cubicboron nitride. This super hard composite material may also incorporate abinder material comprising of cobalt, niobium, titanium, zirconium,nickel, iron, tungsten, tantalum, molybdenum, silicon, a refractorygroup metal or combinations thereof which may bind together grains ofthe super hard composite materials in such a way to form the segments.The interior portion of the segments may thus comprise a region depletedof the binder material. This may be advantageous when the second bore102 is subjected to high temperatures since the binder material may havea higher thermal expansion rate than the superhard composite material.The super hard geometric segments 103, which may be annular segments,wedge like segments, various geometric shape segments or a combinationthereof, may be interposed within the first bore 101 in a concentricarray that extend lengthwise along the longitudinal axis 106 of thefirst bore 101. The super hard composite material may be chemicallyinert and may possess fracture toughness, thermal shock resistance,tensile strength, and low thermal expansion characteristics all of whichmay serve to further enhance resistance to wear when high pressures orhigh temperatures are exerted on the interior surface 104 of thestructure. While not limited thereto, polycrystalline diamond may be thepreferred composite material and may possess a plurality of grainscomprised of a size of 0.1 to 300 microns. The super hard compositematerial may also have a thermal expansion coefficient of approximately2 μin/in, but in some embodiments, the thermal expansion coefficient maybe 0.1 to 10 μin/in. This is a significant feature as it enhances thestructural integrity of the overall structure during periods of highpressure and high temperatures in such applications as a gun barrel,piston cylinder, pipe, tube, or other rigid composite structures thatmay exert friction on the interior surface. Despite the various forcesthat may act on the super hard interior surface 104, the second bore 102is able to retain its structural integrity due in part to the inherentcharacteristics of the super hard geometric segments 103 disposed withinthe first bore 101.

The first bore 101 may be formed in a suitable metallic material thatexhibits lower coefficients of thermal expansion at lower temperaturesand higher coefficients of thermal expansion at higher temperatures suchas Invar 365. Other suitable metallic materials that may be used includebut are not limited to aluminum, titanium, a refractory metal, steel,stainless steel, Invar 36, Invar 42, a composite, a ceramic, carbonfiber or combinations thereof. These materials may exhibit suchcharacteristics that allow the first bore 101 to be manipulated underhigh temperature and then shrink wrapped around the second bore 102.This process may be used in order to hold the super hard geometricsegments 103 under radial compression of 50-200% of operating pressureand axial compression of 50-200% of proof pressure being achievedthrough incorporation of a shoulder 105 at the first end 107 of thefirst bore 101 and biasing unit 108 at the second end 109. Although notlimited to, the metallic material may be Invar 365 due to itscomparative characteristics with polycrystalline diamond which allowboth the first bore 101 and second bore 102 to compliment one another intheir utility and to further enhance the structures ability to retainits structural integrity during periods of high pressures and hightemperatures.

Although the thickness of the super hard composite material may becomparable to the thickness of the metallic material, it should be notedthat in embodiments where the structure comprises a gun barrel, thepreferred thickness for the super hard composite material is 0.040inches to 0.25 inches, while the thickness of the metallic material is0.25 inches to 0.75 inches. The thicknesses of the materials depends onmany factors and any combinations of thickness are covered within thescope of the claims.

FIGS. 2-5 depict various configurations of the super hard geometricsegments 103 that may comprise natural diamond, synthetic diamond,polycrystalline diamond, single crystalline diamond, or cubic boronnitride that may also incorporate a binder material of cobalt, niobium,titanium, zirconium, a refractory group metal or combinations thereof.Each segment may comprise a substantially annular shape, a substantiallywedge shape, a substantially circular or semi-circular shape,substantially curved shape 150, a substantially hexagonal shape 151, asubstantially rectangular shape 152, a substantially trapezoidal shape,or a substantially octagonal shape 153.

In a preferred method for manufacturing super hard geometric segments103, diamond or cubic boron nitride grains are sintered in a hightemperature high pressure press to form the desired shape of thesegment. Usually a binder material is used to catalyze the sinteringprocess, a preferred binder material being cobalt, which diffuses underthe high pressure and temperature from adjacent material (typicallytungsten carbide) also in the press. In such a method, a bond will formbetween the adjacent tungsten carbide and the sintered diamond. FIGS.6-8 depict the processes whereby the segments may be connected and heldin place to form the second bore 102. Referring to FIG. 6, the superhard geometric segments 103 are brazed together using an interfacingmaterial 154 that may comprise of gold, silver, a refractory metal,carbide, tungsten carbide, a cemented metal carbide, niobium, titanium,platinum, molybdenum or combinations thereof. Preferably, theinterfacing material 154 is a tungsten carbide that has bonded to thesuper hard segment during sintering. The abutting ends 155 and 156, maybe formed while still in the press. In FIG. 6, the abutting ends 155,156 comprise a flat shape 1000. In some embodiments a pattern 9000 maybe formed in the interior surface 104 of the segments while still in thepress, such as the rifling patterns for embodiments where the structurecomprises a gun barrel. FIG. 7 discloses an interfacing material 154comprising an annular shape 3000. The annular shape 3000 is bonded in arecess area 157 formed in the abutting ends 155 and 156 of the segments103. The segments may then be brazed together using the interfacingmaterials adjacent the abutting end of the segments. In someembodiments, the segments may be heat treated or annealed during and/orafter they are brazed together, which may be advantageous since stressescreated by brazing may be reduce or eliminated from the interior surface104. In some embodiments the segments may be annealed or heat treatedafter being formed in the press. In embodiments, where a projectile orbullet is propelled through the structure, the presence of a solid brazebetween interfacing materials 154 may increase friction. Also theinterfacing material 154 may thermally expand faster than the super hardgeometric segments 103 which may create stress in the interior surface104 if an interfacing material is present. FIG. 8 discloses a non-planarinterface 2000 between the abutting end 155 and the interfacing material154.

FIG. 9 is a diagram of another embodiment of the present inventionwhereby the segments 103 may be configured in such a way that they arejoined by interlocking profiles. A first abutting end 160 may comprise aprotrusion 4000, which may be fitted within a socket 159 of a secondabutting end 161. In some embodiments, a plurality of protrusions 4000and sockets 159 may be used. In other embodiments, the protrusion 4000may comprise a pointed shape, a conical shape, a curved shaped, arectangular shape, a pyramidal shape, or combinations thereof and thesocket 159 matches the profile of the protrusion. This feature may beincorporated to further ensure that the segments 103 do not rotatewithin the first bore 101 as a result of exposure to high temperaturesand high pressures on the second bore 102. This feature may proveespecially useful if the present invention is adapted for use in theapplication of a gun barrel where movement of the segments maydetrimentally affect the trajectory of a bullet as it exits the barrelbut may be significantly reduced if interlocking abutting ends areincorporated in the formation of the second bore 102 as depicted. Theinterlocking profiles may help align the rifling formed in the interiorsurface 104 of the second bore 102 if the rifling is formed prior toconnecting the segments 103.

FIG. 10 is a diagram of another embodiment of a rigid compositestructure adapted for use as a gun barrel 120, constructed in accordancewith this invention. While this invention may be described in connectionwith a gun barrel it should be noted that it is not restricted to thisuse and has multiple applications in any formation or construction as arigid composite structure that retains its structural integrity duringperiods of high temperatures and high pressures. Other such structuresmay include piston cylinders, tubes or pipe. A gun barrel 120 maycomprise of a first bore 101 formed in a metallic material such assteel. A second bore 102 formed in super hard geometric segments 103,those preferably being made of polycrystalline diamond, may be disposedwithin the first bore 101. The segments may be held under radialcompression, as depicted by arrows 110, by the first bore 101 and axialcompression, as depicted by arrows 111, by the shoulder end 105 and thebreech component 200. A throat 201 and free bore 202 may be made of ametallic material as well as a breech end 203, which may be convenientlythreaded for reception into a breech receiver 204. The breech receivermay apply the axial pressure. In some embodiments the exit end of thestructure may be adapted to receive another threaded receiver whichcooperates with the breech receiver to apply the axial compression tothe segments.

FIG. 11 is an exploded diagram of the aforementioned embodiment in FIG.9 as a gun barrel 120. In some embodiments, the metallic material of thefirst bore 101 will be thermally expanded such that the segments may beinserted into the first bore 101 as a single unit. In other embodiments,the segments 103 may be aligned within the first bore 101. Invar 365 maybe an ideal metallic material since it may expand significantly undervery high temperatures which would allow the first bore 101 to beexpanded for insertion of the segments, but Invar 365 may notsignificantly expand under the range of temperatures that the interiorsurface 104 of the second bore 102 will be exposed to under rapid gunfire allowing the first bore 101 to maintain radial compression 110 onthe segments. After the segments are inserted into the first bore 101,the temperature of the second bore 102 may be lowered to shrink thefirst bore 101. In some embodiments, the intermediate material may bewrapped around the segments prior to their insertion into the firstbore.

In some embodiments, the breech receiver 204 will be threaded into placein the breech end 203 after the first bore 101 is sufficiently cooled.In other embodiments, the breech receiver 204 is not threaded, but isplaced within the first bore 101 such that it biases the segmentsagainst the shoulder 105 of the first end 107, thereby applying an axialcompression 111. Then the temperature of the first bore 101 is lowered,shrinking itself around the breech receiver 204 such that the receiveris held in place after cooling and continues to apply axial compression111 to the segments. In yet other embodiments, axial pressure 111 may beapplied by a biasing unit 108 while the first bore 101 is expanded andthe biasing unit 108 is then removed after first bore 101 is shrunk andthe friction between the first and the segments is enough to provide theaxial compression 111.

FIG. 12 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120 depicting a variation in the formationof a second bore 102 which may comprise of a single super hard geometricsegment 400. The breech component 200 of the structure may comprise athroat 201, free bore 202, a breech end 203, a breech receiver 204, orcombinations thereof which may be made of a metallic material in wholeor in part.

FIG. 13 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120 with a variation in the formation of thebreech component 200 in which the throat 500 and free bore 501 are madeof at least a portion of a super hard geometric segment 103. This may beadvantageous since the throat 500 and the free bore 501 may be subjectedto high amounts of wear.

FIG. 14 is an enlarged view of the embodiment shown in FIG. 13 depictinga breech component 200 including the throat 500 which may be formed inthe super hard interior surface 104. A shoulder 600 may serve to holdthe cartridge 602 in place and from entering the barrel. In someembodiments, the cartridge 602 may be rimmed, rimless and straightbored, or rimless and necked. The diagram also depicts a throat 500 andfree bore 501 formed in at least one of the super hard segments. Theview depicts the throat 500 as it tapers in until the diameter issubstantially equal with the rest of the interior surface 104 of the gunbarrel. The throat may assist to guide the bullet 601 into the barrel.

FIG. 15 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120 with a variation in the formation of abreech component 200 in which a throat 500 and free bore 501 may beentirely made of super hard composite materials. The embodiment alsodepicts at least one port 112 through the first bore 101 and the superhard interior surface 104 which may help to counteract recoilingeffects. The ports may comprise a variety of geometries such as straightbores, tapered bores, rectangular bores, curved bores, angled bores, orcombinations thereof. The ports may comprise a port axis that is normalto the axis of the composite structure or the port access may intersectthe axis of the composite structure at any angle.

FIG. 16 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120. This embodiment may comprise of anadditional intermediate layer 700 which may comprise of a material witha low thermal expansion rate such as Invar 36, Invar 42, and Invar 365,a composite, a ceramic, a refractory metal, carbon fiber or combinationsthereof. The intermediate layer 700 may be wrapped between the firstbore 101 and the super hard geometric segments 103 and serve as athermal insulator to further enhance the structural integrity of thestructure by assisting to contain the detrimental affects of heat on thestructure. A thermal insulator may be advantageous in embodiments, wherethe metallic material of the first bore 101 would thermally expandwithin a temperature produced during gun fire and help prevent heat fromreaching the first bore 101 and allow the radial compression 110 on thesegments to be maintained. Further, an intermediate layer 700 with a lowco-efficient of thermal expansion may also be used as the intermediatematerial. In such an embodiment, the intermediate layer 700 may comprisea high or low thermal conduction rate, but since the intermediate layer700 may not expand even if the first bore 101 does, the radialcompression 110 may be maintained. Also, the thermal conductivity of asuperhard segment made of diamond or cubic boron nitride is much higherthan standard steels typically used for gun barrels the friction of thebullet traveling down the barrel may be lower allowing highervelocities.

FIG. 17 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120. This embodiment may comprise a threadedreceiver 800 which may be comprise a material selected from the groupconsisting of aluminum, titanium, a refractory metal, steel, stainlesssteel, Invar 36, Invar 42, Invar 365, a composite, a ceramic, carbonfiber and combinations thereof at the first end of the first bore 101which may serve to hold the super hard geometric segments 103 in placeand apply axial compression 111.

FIG. 18 is a diagram of another embodiment of the aforementionedapplication as a gun barrel 120. This embodiment may comprise of a firstbore 101 that only a portion of which is lined with super hard geometricsegments 103 while still incorporating the threaded receiver 800depicted in FIG. 17 at the first end 107 of first bore 101. The threadedreceiver 800 may bias the segment or segments against an internalshoulder formed in the first bore. Placing the super hard segments atthe near the exit end of the barrel may be advantageous since gunbarrels are subjected to a high amount of wear near its exit end 107.

FIGS. 19 and 20 are diagrams of other embodiments of the currentinvention depicting a method of manufacturing the super hard geometricsegments 103. In such an embodiments, the segments 103 of the super hardcomposite material (preferable made of polycrystalline diamond) may beformed in a high temperature and high pressure press. The diamond grainsare positioned within the press around a pillar 1003 of tungsten carbidewhich helps to mold the diamond segment in an annular shape. A bindermay diffuse from the tungsten carbide into the diamond grains and act asa catalyst. After the solid segment has been formed, the method mayfurther comprise the use of an electrical discharge machine (EDM). Anelectrode 1002 of the EDM may be plunged into the solid segment of superhard composite material 1001 to form a cavity which results in theformation of the interior surface. Preferably, as shown in FIG. 20 afterthe cavity is initially formed by the EDM from one end of the solidsegment to the other end, an EDM wire 1004 may be threaded through thecavity. This may be beneficial since particles of the super hardmaterial are attracted to the EDM wire or electrode and may be removedfrom the segment by pulling the wire through the cavity. Preferably, allof the tungsten carbide is removed such that there is substantially notungsten carbide remaining in the superhard interior surface 104 of thesegment 103. In other embodiment, a geometry of the superhard segmentsmay be formed by abrasive lapping and/or abrasive grinding.

In some embodiments, the pillar may be lined with a high concentrationof binder. In other embodiments a foil, such as a cobalt foil, may bewrapped around the pillar which may help in the diffusion of the binderinto the diamond grains. In yet other embodiments a foil may be placedbetween the diamond grains and the pillar to prevent a creation of astrong bond between the two. Still in some embodiments, the pillar maybe made of salt or the pillar may be lined with salt. A salt pillar witha foil of a desired binder wrapped around it may allow the formation ofa strong annular segment with an easily removable pillar.

FIG. 21 is a diagram of another embodiment of the current invention. Itdiffers from FIG. 20 in that the depicted segment 103 is solid and hasno pillar of another material disposed within it.

FIGS. 22 and 23 are similar diagrams of embodiments of theaforementioned application as a gun barrel 120 depicting a riflingprocess that may be incorporated using an EDM bit 5000 that is movedthrough the barrel and twisted either clockwise or counter-clockwise toform the desired rifling pattern 6000 using various cutting faces 6001and/or 6002.

FIGS. 24 and 25 disclose other embodiments of the aforementionedapplication as a gun barrel 120 which depict a first and a secondrifling pattern 7000, 8000. The first pattern 7000 comprises lands 7001and grooves 7002 formed in the interior surface of the segments. Thesecond pattern comprises a polygonal shape. Both of these patterns maybe formed with the aforementioned EDM. The rifling patterns may beincorporated to assist with the ballistics of a gun barrel as the bulletexits the barrel during ordinance use.

Patterns formed in the interior of other composite structures may alsobe formed using an EDM. It may be desirable that a piston comprise ananti-rotation protrusion and super hard segments lining the bore of thecylinder comprises a complementary slot coaxial with the piston for theprotrusion to travel in.

FIG. 26 is a diagram depicting a method 260 for manufacturing a rigidcomposite structure. The method comprises the steps of providing 261 astructure with a bore, providing 262 a plurality of geometric segmentswith a superhard interior surface, forming 263 a second bore by joiningthe ends of the segments together, thermally expanding 264 the firstbore, placing 265 the second bore within the expanded first bore, andshrinking 266 the first bore around the second bore by cooling.

Whereas the present invention has been described in particular relationto the drawings attached hereto, it should be understood that other andfurther modifications apart from those shown or suggested herein, may bemade within the scope and spirit of the present invention.

1. A rigid composite structure, comprising: a first bore formed in ametallic material and comprising a longitudinal axis; a second boreformed by geometric segments comprising a superhard interior surface,the segments being disposed adjacent one another substantially co-axialalong the longitudinal axis within at least a portion of the first bore.2. The structure of claim 1, wherein the superhard interior surfacecomprises a material selected from the group consisting of naturaldiamond, synthetic diamond, polycrystalline diamond, single crystallinediamond, cubic boron nitride, and composites thereof.
 3. The structureof claim 1, wherein the superhard interior surface comprises region thatis depleted of a binder material.
 4. The structure of claim 1, whereinthe superhard interior surface comprises a binder material selected fromthe group consisting of cobalt, niobium, titanium, zirconium, nickel,iron, tungsten, tantalum, molybdenum, silicon, a refractory group metal,or combinations thereof.
 5. The structure of claim 1, wherein thestructure further comprises an intermediate material between the firstbore and the geometric segments.
 6. The structure of claim 5, whereinthe intermediate material is a thermal insulator.
 7. The structure ofclaim 5, wherein the intermediate material is wrapped around thesegments.
 8. The structure of claim 5, wherein the intermediate materialcomprises Invar 36, Invar 42, Invar 365, a composite, a ceramic, arefractory metal, carbon fiber or combinations thereof.
 9. The structureof claim 1, wherein the metallic material comprises a material selectedfrom the group consisting of aluminum, titanium, a refractory metal,steel, stainless steel, Invar 36, Invar 42, Invar 365, a composite, aceramic, carbon fiber or combinations thereof.
 10. The structure ofclaim 1, wherein the geometric segments are brazed to one another by aninterfacing material selected from the group consisting of gold, silver,a refractory metal, carbide, tungsten carbide, niobium, titanium,platinum, molybdenum, Nickel Paladiium, cadmium, chromium, copper,silicon, zinc, lead, manganese, tungsten, platinum, or combinationsthereof.
 11. The structure of claim 1, wherein the geometric segmentscomprise a non-planar end.
 12. The structure of claim 1, wherein thesuperhard interior surface is made of a plurality of grains comprises asize of 1 to 300 microns.
 13. The structure of claim 1, wherein thesuperhard interior surface is under a radial compression of 50-200% ofoperating pressure.
 14. The structure of claim 13, wherein the radialcompression is achieved by heat shrinking the tube around the superhardinterior surface.
 15. The structure of claim 1, wherein the superhardinterior surface is under an axial compression of 50-200% of proofpressure.
 16. The structure of claim 15, wherein the axial compressionis achieved by providing a shoulder in the first end of the first boreand biasing unit in the second end.
 17. The structure of claim 1,wherein the superhard interior surface comprises a thermal expansioncoefficient of 0.5 to 10 μin/in.
 18. The structure of claim 1, whereinthe tube further comprises a port through the first bore and thesuperhard interior surface.
 19. The structure of claim 1, whereinsuperhard interior surface is polished.
 20. The structure of claim 1,wherein the superhard interior surface comprises a geometry formed byelectrical discharge machining, abrasive lapping or abrasive grinding.21. The structure of claim 1, wherein the tube is a piston cylinder, agun barrel, a tube and/or a pipe.
 22. The structure of claim 21, whereinthe superhard interior surface is disposed within the gun barrel andcomprises rifling with a land and groove or polygonal shape.
 23. Thestructure of claim 22, wherein a free bore of the gun barrel is formedin the superhard interior surface.
 24. The structure of claim 22 whereina throat of the gun barrel is formed in the superhard interior surface.25. A method for forming a rigid composite structure, comprising:providing a structure with a first bore intermediate a first and secondend; providing a plurality of geometric segments with a superhardinterior surface; forming a second bore by joining the ends of thesegments together; thermally expanding the first bore; placing thesegments within the expanded first bore; and shrinking the expandedfirst bore around the segments by cooling.
 26. The method of claim 25,wherein a geometry of the superhard segments is formed by electricaldischarge machining, abrasive lapping or abrasive grinding.